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Re: [Amps] Relays

To: "'amps'" <amps@contesting.com>
Subject: Re: [Amps] Relays
From: John/K4WJ <k4wj@bellsouth.net>
Date: Wed, 02 Apr 2008 09:50:41 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I use a DEO QSK-1500 for my QSK operations. This is a PIN diode unit 
that K8RR and W4TV designed back in the 80s. It was rather expensive 
in those days but there are a few of them out there that can be 
purchased in the $150 to $200 range. I have two QSK-1500 units, but 
one needs repair.


I've discovered that some of the sellers are elderly and have abused 
their units to the point that some repair is necessary. However, they 
are very easy to trouble shoot and can be repaired rather cheaply 
unless the main transmit PIN is damaged. Then it becomes a rather 
huge task trying to locate one of these PINs. (It is rare for them to 
be damaged.)

I did a poor job of matching my antennas to the transmission line so 
I use a TenTec 238 to bring the SWR down to a level that doesn't 
bother the QSK-1500. I use the QSK-1500 with a TenTec Omni VI Plus 
and either a Ameritron ALS-600 or an old Alpha 77, which is currently 
on the fritz.

One plus for using PIN diodes is that they are silent.

I have no idea what Alex is talking about when he mentions that they 
operate as a noise diode. I can't tell the difference in the received 
signal between having the QSK-1500 in the transmission path or 
by-passed. I can copy the weakest DX signals. However, I've never 
taken any noise measurements with the unit in or out of the receive 
path, I'm only going by what my ears tell me.

I LOVE my QSK-1500s.

73..de John/K4WJ


At 02:41 AM 4/2/2008, Alex wrote:
>Hi guys:
>It so happens that during the last 2 years or so I worked on high power
>amplifiers in the kilowatt range .
>PIN diodes are made by very few manufacturers, coming and going all the
>time. They can run In the 300$ dollars range, are susceptible to burn out at
>mediocre SWR,s and require back bias voltage approximately 3 times the PTP
>RF voltage involved. They also require a forward current of a few hundreds
>of mA to conduct well when open. This adds directly to the input noise
>because they operate as a noise diode would.
>In short, if you don't need fast switching speeds, don't mess with them.
>They also have only a poor isolation of around 30 dB. In QRO use the
>leftover power at the receiver port is still to much so that you need some
>additional switching after the main diode with associated driving circuits.
>In short, drop it!!!
>73 and all the best:
>Alex    4Z5KS
>
>-----Original Message-----
>From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>Behalf Of Kim Elmore
>Sent: Wednesday, April 02, 2008 4:48 AM
>To: amps
>Subject: Re: [Amps] Relays
>
>Thanks, Vic!  Makes perfect sense. Yes, the PIN diodes are quite
>expensive, especially for ones capable of handling much power.
>
>73,
>
>Kim N5OP
>At 06:28 PM 4/1/2008, you wrote:
> >Kim Elmore wrote:
> >
> > > But, this does lead to a question: are PIN diodes avoided simply
> > > because using them is far more complex than relays, or is there some
> > > other reason they aren't often used?
> >
> >The cost of the diodes and associated circuitry is more than a cheap
> >relay. And they are susceptible to damage from lightning-created
>transients.
> >
> >I had an Alpha 86 with pin-diode switching that worked great. Never any
> >problems. But a lot of Alpha users did have problems and at some point
> >they started using vacuum relays. Someone who can afford a newer Alpha
> >can tell us if they still do!
> >--
> >73,
> >Vic, K2VCO
> >Fresno CA
> >http://www.qsl.net/k2vco
> >_______________________________________________
> >Amps mailing list
> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
>
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73..de John/K4WJ
ex K8PXG 18 Jun 1959 to 11 Feb 1997
K8WJ 12 Feb 1997 to 08 Apr 1997


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